test: Fix Windows screenshots

Since upgrading to Chromium-based Edge, some slight rendering changes
have thrown off our screenshots.  In some, the shade of green in the
background has changed slightly.

This slightly increases the threshold for detecting individual pixel
changes, so that most of these tiny shade changes now pass.

In one other case, a change in the outline of the green-on-blue test
required an actual screenshot update for both Chrome and Edge on
Windows.

Change-Id: I413f927e3d3a00b8369600808392c6b05a185d54

build/pixelsChanged.js

@@ -24,7 +24,7 @@ const Jimp = require('jimp');
 async function main(oldPath, newPath) {
   const oldImage = await Jimp.read(oldPath);
   const newImage = await Jimp.read(newPath);
-  const diff = Jimp.diff(oldImage, newImage, /* threshold= */ 0);
+  const diff = Jimp.diff(oldImage, newImage, /* threshold= */ 0.07);
   // "percent" is, surprisingly, a number between 0 and 1, not between 0 and
   // 100.  Convert this to a number of pixels.
   const pixelsChanged =

karma.conf.js

@@ -589,7 +589,7 @@ function WebDriverScreenshotMiddlewareFactory(launcher) {
     // browser can cause failures even when a human can't see the difference,
     // and setting it too high means human-noticeable changes could go
     // undetected by a test.
-    const diff = Jimp.diff(oldScreenshot, newScreenshot, /* threshold= */ 0.05);
+    const diff = Jimp.diff(oldScreenshot, newScreenshot, /* threshold= */ 0.07);
 
     // Write the diff to disk.  This is used to review when there are changes.
     fs.writeFileSync(